Seat belt force sensor

ABSTRACT

A force-sensing mechanism ( 20 ) comprising: a housing having first ( 22 ) and second ( 24 ) housing members; a slidable plate positioned between plate portions of the first and second housing members and moveable thereto; various spacers located between the first housing member and the sliding plate to space and stabilize the plate relative to the first and second housing members; a magnetic sensor stationarily mounted between the first and second housing members, a magnet moveable with the sliding member in response to forces applied to the first and second housing members and to the sliding plate; a spring assembly ( 250 ) having one end in operative engagement with the sliding plate and another end in operative engagement with the housing while biasing the sliding plate within the housing. An adjustment mechanism ( 350 ) is used to assist in the calibration of the bias force acting between the housing members and the sliding plate.

The present application is a continuation in part of the U.S. Ser. No.09/597,042 (filed Jun. 20th, 2000) now U.S. Pat. No. 6,400,145B1, whichis related to a provisional patent application No. 60/202,162, filed May4, 2000.

BACKGROUND AND SUMMARY OF THE INVENTION

The invention generally relates to force sensing mechanisms and moreparticularly to one such sensor capable of measuring the tensile forceproduced within a buckled-up seat belt system and more particularly thelap belt.

The present invention is an improved force sensing mechanismcharacterized by low dead zone, hysteresis and sliding friction, ease ofassembly and reduced cost.

It is a further object of the present invention to provide a forcesensor or force sensing mechanism that is usable in cooperation withother sensors (including a weight sensor) to determine the normal forceon a vehicle seat, which is produced in part by the weight of the objector person on the seat and the tension within a seat belt system.

The present invention defines an electronic force sensor for use in aseat belt system. The sensor includes a number of interconnected parts,some of which are relatively movable and mutually spring loaded. As aresult of manufacturing tolerances the electrical output of the sensor,which follows its force-deflection characteristic, may include a deadzone or may display hysteresis. It is an object to provide a forcesensor that includes a compensating feature to reduce or otherwiseeliminate dead zone and/or hysteresis.

Accordingly the invention comprises: a force-sensing mechanismcomprising: a housing, which can include first and second housingmembers; a slidable member or plate positioned within the housing suchas between portions of the first and second housing members and moveablethereto; various spacers located between the housing and the slidingplate to space and stabilize the sliding plate relative to the first andsecond housing members; a magnetic sensor stationarily mounted betweenthe first and second housing members, a magnet moveable with the slidingplate in response to forces applied across the housing and to thesliding plate; a spring assembly having one end in operative engagementwith the sliding plate and another end in operative engagement with thehousing to bias the sliding plate within the housing. The springassembly includes an adjustment mechanism that is used to calibrate theforce sensor and in calibrating the sensor, the dead zone is eliminatedand hysteresis reduced or eliminated. This adjustment mechanism createsa greater uniformity from sensor to sensor.

Many other objects and purposes of the invention will be clear from thefollowing detailed description of the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded view of a force sensing mechanism in accordancewith the present invention.

FIG. 2 is a plan view of the bottom of a force sensor.

FIG. 3 is a cross-sectional view through section 3—3 of FIG. 2.

FIG. 4 is a cross-sectional view through section 4—4 of FIG. 2.

FIG. 5 is a cross-sectional view through section 5—5 of FIG. 2.

FIG. 6 is a cross-sectional view through section 6—6 of FIG. 2.

FIG. 7 is a cross-sectional view through section 7—7 of FIG. 2.

DETAILED DESCRIPTION OF THE DRAWINGS

Reference is made to FIGS. 1-4, which illustrate the major components ofa seat belt force sensor or sensing mechanism 20 which include: ahousing having an upper housing member 22, a lower housing member 24 anda slide or sliding member 26. In the embodiment shown in FIG. 1, thehousing members 22 and 24 are identical. Consequently, only one physicalpart need be produced as it can be used in both the upper and lowerhousing position. Further, in the preferred embodiment, the housingmembers 22 and 24 and the slide 26 are fabricated as stamped steelcomponents, each having a coating to prevent corrosion and provide auniform, smooth surface finish. Each of the housing members 22 and 24includes a plate portion 28 and an anchor portion 30. The anchorportions 30 are secured to a structural component of the vehicle such asthe floor or seat, generally shown by numeral 32 (in FIG. 1), through ananchor mechanism, which is also schematically shown by numeral 34. Theseanchor mechanisms can, for example, include a cable attached at onecable end to the anchor portion 30 and at the other cable end to astructural section of the vehicle or the seat, to a seat beltpretensioner or alternatively, a fastener received through the openings36 in the anchor portions. The anchor can be designed to permit theforce sensor to rotate or move in one or more directions.

Reference is briefly made to FIG. 3, which is a cross-sectional viewtaken through the center of the mechanism 20. As can be seen from FIG.3, the anchor portions 30 mate with each other while the plate portions28 of the upper and lower housing are spaced apart with the movable orsliding plate 26 positioned therebetween. Each housing portion 22 and 24includes a ramped transition surface 40 connecting the portions 28 and30. Each of the plate portions 28 is generally rectangular in shapedefining a central opening 42. A first end 44 of each plate portionincludes a central opening 46 through which is received a rivet 48. Therivet extends through an optional hardened steel bushing or sleeve 50,which assists in spacing the opposing plate portions apart and alsoserves as a mechanical stop to limit the outward extreme movement of thesliding plate 26. If the bushing 50 is not used, its function isperformed by the shaft 52 of the rivet. End 44 includes two oblongopenings 54 a and 54 b. Each of the plate portions further includes afirst side 56 and a second side 58. Each plate portion additionallyincludes a second or opposing end 60, with a recessed portion (seenumeral 62) recessed below the plane of the first and second side andfirst end. The first side 58 further includes a bent tab 64, whichincludes a forked end 66, which is bent over (swaged) during finalassembly to secure the housing portions 22 and 24 together. Prior tobending over end 66, these ends are received within correspondingopenings 70 in the opposing upper and lower housing members, as well aswithin a corresponding spacer 180 (which also serves as a guide).

Each of the housing members 22 and 24 includes an upraised bridgeelement 72, which extends above the plane of the first and second sides56 and 58 of the plate portion 28. Each bridge element includes a flat,extended surface 74, which includes an opening 76. Each of the bridgeelements also includes a small notch 80 adjacent opening 42 and anoppositely positioned larger notch 82. These notches 80 and 82 are usedto capture facets of a sensor housing 90.

The sliding plate 26 includes a first oval opening 100, situated nearend 102. It is this end of the plate that is secured to a connector orconnecting member 104, such as a length of seat belt webbing, that is inturn connected or secured to a conventional seat belt buckle, generallyshown as 106. If a flexible seat belt webbing 104 is used as thisconnector or connecting member 104, then an insert 104 a is insertedwithin opening 100 to protect the seat belt webbing 104 from any sharpedges that may exist about the opening 100. Positioned to the rear (thatis, to the left in FIG. 1) of the opening 100 is an oval opening 110.Positioned on either side of the oval opening are rectangular or ovalopenings 112 a and 112 b, each of which has a length sufficient to notinterfere with the motion of the sliding plate before it reaches itsmaximum excursion limited by the oval opening 110 and spacer 50.Positioned rearward of the oval opening 110 is a larger opening,generally identified by numeral 120. This opening has a first part 122and a second part 124. The width of this second part or opening 124 isnarrower than the width of opening 122. Additionally, it should be notedsides 130 and 132 of plate 26 are narrowed at numerals 134 and 136. Theslide or sliding plate 26 also includes projections 140 and 142, whichextend into opening 120.

In order to prevent binding of the sliding plate 26, the sensingmechanism or sensor 20 further utilizes two identically shaped inserts,both of which are shown by numeral 150 (also shown in FIG. 4). Each ofthe inserts 150 includes a first surface 154 having a plurality ofrectangular projections 156 a and 156 b, extending therefrom. As can beappreciated, surface 154 of the lower insert 150 is not visible in FIG.1. Each of the projections 156 a and 156 b is received within acorresponding opening 54 a and 54 b in each of the housing members.Preferably the projections 156 a and 156 b are tightly received withinthe corresponding openings. Each of these inserts includes a second setof projections 158 a and 158 b extending from another surface 160. Theprojections of each two insert pieces 150 nest with each other to ensurethey are aligned laterally and vertically as shown in FIG. 4. Extendingfrom surface 160 is a plurality of small tabs 161. Additionally, eachinsert includes an oval-shaped slot 162 that is sized to prevent theinsert (when it is in place on its respective housing member 22 or 24)from interfering with the rivet 48 and/or sleeve 50. Each of theprojections 158 a and 158 b is received into the top and bottom ofopenings 112 a and 112 b of the plate 26. As can be appreciated fromFIG. 3, the projections 150 a and 150 b, after insertion within theopenings 112 a and 112 b, mate with each other and, as can be seen,these inserts as well as the bushing maintain the spacing between theupper and lower housing members. Additionally, the tabs 161 provide fora low-friction surface upon which the sliding plate 26 can slide and,further, the projections 158 a and 158 b laterally stabilize the plate26.

The opposite ends 60 of each of the housing members 22 and 24 are spacedapart by the step on tab 64. A pair of spacers 180 assist in the spacingof the members 22 and 24 but are designed not to take high loads, whichare absorbed by each tab 64. Each spacer 180 includes each alongitudinal slot 182, which is respectively received on side 134 and136 of the plate 26. Additionally, each spacer includes a vertical slot184 (as seen in FIG. 1). During assembly, a corresponding tab 64 fromeach of the housing members 22 and 24 is first received through opening184 prior to being received within the corresponding opening 70 in theopposing housing member. The spacers 180 laterally stabilize the rearend of the plate 26 and also provide a low-friction surface upon whichsides 134 and 136 can slide. As mentioned above, the sensor mechanism 20includes a sensor housing 90. The housing 90 includes a cup-shaped body200 having side walls 202 and a bottom 204. Extending from the bottom isa projection 206, which is received within opening 76 of the lowerhousing member 24. One of the walls 202 includes an upraised tab 210,which is received within groove 80 of the upper housing member. Thesensor housing 90 further includes a rearwardly extending ledge 212,which includes on an upper surface thereof tabs 214 a and 214 b. Thevertical surfaces 216 a and 216 b of tabs 214 a and b are receivedwithin the groove 80 of the upper housing member 22 while the rearsurface 216 of the extending ledge 212 rests against the side 218 of thedepressed portion 62 of end 60 of the plate portion 28 of the upperhousing member 22. In the illustrated embodiment, a Hall effect sensor230 is received within the sensor housing 90. The Hall effect sensor andits conditioning electronics 231 can provide an analog signal indicativeof the spacing and hence the force applied to the sensor sensingmechanism. In other applications a continuous analog signal is notneeded and a digital Hall effect sensor can be used. As used herein adigital Hall effect sensor would be a conventional Hall effect sensorwith a threshold established by associated electronics 231 such that theHall effect sensor (and its electronics) will only generate an outputsignal if the applied force and hence the magnetic field exceeds thethreshold level.

The force sensing mechanism 20 further includes a spring subassembly250, part of which holds a magnet 252. The spring assembly 250 includesa first support or plate 254 having two sets of laterally extendingwings 256 a and 256 b and 257 a and 257 b. The sets of wings are spacedapart by a distance designated by numeral 258. The rear surface of plate254 includes a recess 260 into which the magnet 252 is received. Thefront or opposite surface includes a circular projection 262 that isreceived within the inner diameter 264 of a compression spring 266. Ascan be appreciated, the circular projection 262 stabilizes the rear endof spring 266. Positioned on the other side of spring of 266 is anothersupport or plate 280 having two sets of wings 282 a and 282 b and 283 aand 283 b. Each of the sets of wings 282 a and 282 b is spaced apart bya distance shown by numeral 284. Support 280 further includes amechanical adjusting mechanism 350. The support mechanism 280 includes aprojection 290, which is also part of the adjustment mechanism 350. Theprojection includes threads 354 and is sized to fit within the centerspace 264 of the spring 266. The adjustment mechanism 350 also includesa nut or wheel 360 having internal threads 362. The wheel 360 is mountedto and rotatable about the threaded projection 290. A flat side 364 ofthe nut or wheel 360 is adjacent end 266 a of the spring 266. The nuttranslates relative to the spring 266 as the nut 360 is rotated on thethreads of the projection 290.

The supports or plates 254 and 280 and the spring 266 are receivedwithin the major diameter opening 122 of plate 26. The projectionsprovide positional guidance. Additionally, portions of these supports orplates 254 and 280, spring 266 and wheel 360 extend into the openings 42in the upper and lower housing members. The wheel 360 can extend beyondthe housing members 22 or 24. In the preferred embodiment the wheel 360is about even with the housing members 22 and 24. When the rear supportor plate 254 is received within opening 122, the pairs of wings 256 aand 256 b envelop the inner wall 122 of the sliding plate 26. The frontsupport 280, while being received within opening 122, actually ridesupon the exterior surfaces of the upper and lower housing members. Moreparticularly, the spacing 284 between each set of wings 282 a and 282 bis sufficient to permit each wing of these respective sets of wings toslide on the top and bottom surfaces of the upper and lower housingmembers. The spring 266 is mounted, as mentioned above, such that end264 is received about the circular boss 262, while its opposite end isreceived about the projection 290 on support 280.

During the initial assembly of the spring 266 onto the projection 290the nut 360 is rotated to a position that is clear of (or at least verylightly contacting) the end 266a of the spring 266. In this way thespring can be installed in a relaxed condition. Thereafter the nut 360is rotated to a desired position, as discussed below, compressing thespring 266. As the spring 266 compresses, the slide 26 is biasedrearwardly between the upper and lower housing members 22 and 24.

As can be seen, spring 266 biases plate 254 rearwardly so that supportor plate 254 bottoms against an adjacent wall of the sensor housing asmore clearly shown in FIG. 2. The spring 266 also biases support orplate 280 forwardly (or rightwardly in FIG. 1), which pushes the forwardsurface of the support or plate 280 against the surface 292 at theforward ends of openings 42.

Depending on at least the stack-up of tolerances of the various parts ofthe sensor 20 the spacing between the spring supports or plates 254 and280 will vary. Additionally, the length of the spring 266 might beslightly off-nominal. Consider for the moment a sensor that does notinclude an adjustment mechanism or feature 350. If for example thespacing is too small or the spring length is too long, the pre-loadforce biasing the slide 26 and the housing members 22 and 24 apart willvary from one sensor to the next. A different though similar result willoccur if the above dimensions were reversed. Additionally, the variationin part size may also create a dead zone of unknown size.

The calibration process uses the adjustment mechanism 350 to provide amore uniformly operating sensor mechanism. As mentioned, the wheel 260is initially placed at a non-contacting or lightly contacting locationin which the spring 266 is at its relaxed length. To speed assembly, thenut 360 can be pre-positioned based upon empirical data or it can simplybe manually positioned apart from or near the spring. Thereafter, thenut 360 is rotated to compress the spring 266 until the bias force ofthe spring 266 is at a determinable level. During calibration of theforce sensor 22 the actual bias force is measured by introducing anaccurate measuring device or calibration force sensor 380, such asbetween the supports 254 and 280. The location of contacting ormeasurement arms 382 a and 382 b of the calibrating sensor 380 inrelation to the supports 254 and 280 is shown schematically in FIG. 2.The wheel or nut 360 is rotated until the calibration sensor 380 readsabout 0.5 Kilo (about 1 pound) which is the desired bias force of thespring 266. This process insures that the housing members 22 and 24 andthe slide 26 will be uniformly biased from sensor to sensor and thisprocess will also eliminate any dead zone. After the force sensor 20 ismechanically adjusted, the calibration sensor is removed and used tocalibrate another force sensor. As can be appreciated, the above methodand apparatus compensates for the stack-up of tolerances due to the manyparts used within the force sensor 20 and compensates for variabilityfrom sensor-to-sensor. After having calibrated the spring force the nutis fixed in place such as with a liquid thread lock.

As can be appreciated, the slide 26 and housing will begin to move apartafter the applied force differential exceeds the calibrated bias.

In some situations after mechanically calibrating the spring bias level,the null output of the Hall effect sensor may be other than desired(zero or otherwise). To more accurately set the null position, and asmentioned above the support 254 (which carries the magnet 252) buttsdirectly against the sensor housing 90 which houses the Hall effectsensor 230. The output of the Hall effect sensor 230 at its nullposition might vary from its preferred output level also due to themanufacturing tolerances of the mating parts. If desired, the effectiveoutput of the Hall effect sensor can be driven to the preferred level(including zero or another value) by analog or digital compensation. Forexample, a bias voltage can be added (plus or minus) to the conditionalelectronics 231 to adjust the output signal to the preferred level.Alternately, an off-set digital value can be added to the Hall effectoutput in a related computer and control (storage) module.

As a force is applied by the seat belt 104 to end 102 of the slidingplate 26, the plate moves outwardly relative to the housing members 22and 24 against the bias force of the spring 266 as the anchor portions30 are held fixed. As the force increases, the spacing between themagnet 252 and the sensor 230 varies, thereby providing a measure of thedisplacement between the stationary sensor 230 and the moveable magnet252, which is directly correlatable to the force applied by the seatbelt. The size of the oval opening 110 and the adjacent openings 112 aand 112 b are sized such that, with exceptionally large forces, thesliding plate 26 is permitted to move outwardly until the inner surface302 abuts a corresponding surface of the sleeve 50, which defines themaximum range of motion of the sliding plate.

Many changes and modifications in the above-described embodiment of theinvention can, of course, be carried out without departing from thescope thereof. Accordingly, that scope is intended to be limited only bythe scope of the appended claims.

What is claimed is:
 1. A force-sensing mechanism (20) comprising: ahousing (22, 24); a plate (26) axially movable in relation to thehousing along a first axis; a magnetic sensor assembly including amagnet sensor (230) and a magnet (252) relatively movable to oneanother, on the first axis, in response to forces applied to the housingand to the plate; a spring assembly (250) having one end in operativeengagement with the plate and another end in operative engagement withthe housing to provide a bias force, directed along the first axis toresist movement of the plate in response to forces applied thereto; andan adjustment mechanism operatively connected between the housing andthe plate, in colinear alignment with the first axis, to enable thecalibration of the sensor and calibration of the force of the springassembly (250).
 2. The sensor mechanism as defined in claim 1 whereinthe adjustment mechanism includes a rotatable and translatable member incontact with one end of a spring of the spring assembly for adjustingthe bias force to a preferred level.
 3. The sensor mechanism as definedin claim 1 including a mechanical stop for preventing movement of theplate in a first direction.
 4. The sensor mechanism as defined in claim3 wherein one mechanical stop is achieved by having a support plate(254) butt up against a magnet sensor housing.
 5. The sensor mechanismas defined in claim 1 wherein the adjustment mechanism is centrallylocated within one of the plate and the housing.
 6. The sensor mechanismas defined in claim 1 wherein the adjustment mechanism is within anopening in the plate.
 7. A force-sensing mechanism (20) comprising: ahousing (22, 24); a plate (26) slidably movable in relation to thehousing; a magnetic sensor assembly including a magnet sensor (230) anda magnet (252) relatively movable to one another in response to forcesapplied to the housing end to the plate; a spring assembly (250) havingone end in operative engagement with the plate and another end inoperative engagement with the housing to provide a bias force to resistmovement of the plate; and an adjustment mechanism operatively connectedbetween the housing and the plate to enable the calibration of thesensor; wherein the housing includes: first (22) and second (24) housingmembers, each of the first and second housing members includingrespective plate portions (28), which are spaced apart; and wherein theplate (26) is positioned between the plate portions of the first andsecond housing members and moveable thereto; first and second spacers(150), a first spacer received between the first housing member and theplate and a second spacer received between the second housing member andthe plate to space and stabilize the plate relative to the first andsecond housing members, the first and second spacers are received withincorresponding apertures (112 a,b) of the sliding plate 26; third andfourth spacers (180) positioned between the first and second housingmembers, each of the third and fourth spacers including a longitudinalslot (182) thereon to receive a corresponding portion of the plate, eachof the third and fourth spacers including slots (184) that are orientedgenerally perpendicular to the direction of movement of the slidingplate.
 8. The sensor mechanism as defined in claim 7 wherein an end ofthe housing, which receives the first and second spacers, is securedtogether by a rivet assembly and wherein the sliding plate includes anoblong opening (110) and wherein the rivet assembly is received throughthe oblong opening (110), wherein the cooperation between the oblongopening and the rivet assembly provides at least one motion stop for thesliding motion of the sliding plate (26).
 9. The sensor mechanism asdefined in claim 7 wherein the adjustment mechanism includes a rotatableand translatable member in contact with one end of a spring of thespring assembly for adjusting the bias force to a preferred level. 10.The sensor mechanism as defined in claim 7 including a mechanical stopfor preventing movement of the plate in a first direction.
 11. Thesensor mechanism as defined in claim 10 wherein one mechanical stop isachieved by having a support plate (254) butt up against a magnet sensorhousing.
 12. A force-sensing mechanism (20) comprising: a housing havingfirst (22) and second (24) housing members; a slidable plate positionedbetween plate portions of the first and second housing members andmoveable thereto; various spacers located between the first housingmember and the sliding plate to space and stabilize the plate relativeto the first and second housing members; a magnetic sensor stationarilymounted between the first and second housing members, a magnet moveablewith the sliding plate in response to forces applied to the first andsecond housing members and to the sliding plate; a spring assembly (250)having one end in operative engagement with the sliding plate andanother end in operative engagement with the housing while biasing thesliding plate within the housing; an adjustment mechanism operativelyconnected between the first and second housing members and colinear withthe spring assembly and magnetic sensor to the calibration of a responseforce of the spring assembly (250).
 13. The sensor mechanism as definedin claim 2 wherein the adjustment mechanism includes a rotatable andtranslatable member to adjust a bias force between the housing membersand the slidable plate.
 14. A force-sensing mechanism (20) comprising: ahousing (22, 24); a plate (26) axially movable in relation to thehousing, along a first axis: a Hall effect sensor for generating anoutput signal and a magnet (252) for producing a magnetic field, theHall effect sensor and the magnet relatively movable one to the otheralong the first axis, in response to axially directed forces applied tothe housing and to the plate, the sensor generating a first level ofoutput signal when no external axial forces are applied to the housingor to the plate; a spring assembly (250) having one end in operativeengagement with the plate and another end in operative engagement withthe housing to provide a bias force, along the first axis, to resistmovement of the plate in response to axial forces applied thereto; andan adjustment mechanism operatively connected between the housing andthe plate to adjust the relative placement of the Hall effect sensor andmagnet to null the output of the Hall effect sensor with no such axialforces applied, the adjustment mechanism having a bearing surfacecoupled to the spring assembly which is configured to adjust the biasingforce of the spring assembly (250) along the first axis.